It is well known to provide a sieve or sieves in the grain cleaning system of an agricultural combine. Typically, the cleaning system will consist of two sieves, an upper or coarser sieve or chaffer located below the threshing mechanism or separator of the combine and having larger sieve openings for the passage of grain and smaller pieces of plant material therethrough but relatively little of the larger chaff, and a lower finer sieve located below the chaffer for receiving the grain and smaller pieces of plant material therefrom and having smaller sieve openings for passage of the grain therethrough but relatively little of the plant material. During operation of the sieves, a flow of air is directed upwardly therethrough for facilitating lifting and carrying away of lighter elements of the plant material from the upper surfaces of the sieves.
A typical sieve construction has an overall generally rectangular shape and includes a plurality of elongate parallel, pivotally mounted, sidewardly extending slats, each slat including a plurality of longitudinally spaced upwardly extending inclined fingers, the slats being pivotable through a range of open positions angularly oriented to horizontal for providing a corresponding range of openings or spaces between the fingers of adjacent ones of the slats. A typical sieve includes an adjusting member which contacts each of the slats, and a linkage and/or cable arrangement connected between the adjusting member and one or more manually or automatically movable adjusting elements or adjustors, in the latter instance, which can be moved by an actuator driven by an electrical, fluid, or other controller for moving the linkage or cable arrangement and member and thus changing the angular orientation of the slats and as a result, the opening size.
The sieves are typically each supported by a correspondingly rectangular shaped welded or fastened assembly commonly known as a sieve rail assembly. The sieve rail assemblies, in turn, are typically supported for rapid reciprocating movement in the fore and aft direction, as driven by a suitable drive element or actuator, such as a powered crank mechanism or the like. For instance, in one common construction the drive is connected in driving relation to the rail assembly supporting the upper sieve or chaffer, which upper rail assembly supports the rail assembly supporting the lower sieve for reciprocating movement opposite to reciprocating movement of the upper sieve. That is, as the upper sieve is driven in one direction, the lower sieve is driven by the upper sieve in the opposite direction.
In operation, grain, and plant and other material other than grain (MOG) will sometimes be deposited on the upper one of the sieves by the threshing mechanism in an uneven manner, particularly as the combine is traversing a hillside, so as to result in uneven loading conditions exerted against both the sieve and the sieve rail assemblies. Air flow upwardly through the sieve may also be uneven. Additionally, there may be some flexing of the structure of the combine supporting the sieve rail assemblies resulting from operation, for instance, from traversing furrows, ditches and other surface irregularities. As a result, the sieves and particularly the sieve rail assemblies are subjected to uneven stress conditions which can cause deformation thereof, particularly racking or parallelogramming of the rectangular shapes, which is a condition wherein the applied forces urge the rail assembly from its normal rectangular shape. Over time, this has been found to result in the development of fatigue cracks in the structural elements of the sieve rail assemblies, particularly, in the corners thereof, which are typically welded joints. The occurrence and/or extent of these conditions have been found to be greater in sieves of larger size, either in length, width, or both, which are used in larger combines, due to the greater crop loads processed by the sieves.
One contemplated option as a possible solution to the racking problem set forth above for retaining the desired rectangular shape of the sieve rail assemblies, has been to utilize large corner gussets for reinforcing the corner joints. However, this option is not favored, as it would result in decreased surface area for grain cleaning and could obstruct upward air flow through the sieves. Also, adding additional mass of large gussets will increase the moving mass of the rail assembly so as to increase the loading conditions exerted against the corner joints.
Accordingly, what is sought is a sieve support structure for an agricultural combine, which overcomes one or more of the problems and shortcomings set forth above.